HBASE-8655 Backport to 94 - HBASE-8346(Prefetching .META. rows in case only when useCache is set to true) (Himanshu and Anoop)

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1488034 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/0.94' into 0.94-gd
Merge remote branch 'origin/0.94-gd' into fb-YAHOO-312-0.94-gd